(CNN) — Sinn Fein leader Gerry Adams was released Sunday after four days in police custody in connection with the 1972 abduction and killing of a mother of 10 by the Irish Republican Army, police in Northern Ireland said.

Adams, 65, has long denied having any role in the death of Jean McConville, a widow who was reportedly killed by the IRA four decades ago because the group believed she was a spy for the British army.

Adams is a prominent Catholic politician who helped broker peace in Northern Ireland and who has long been associated with the IRA, once considered the armed wing of Sinn Fein. Today, Sinn Fein is Ireland’s second-largest opposition party.

“Let me be very clear: I am innocent of any involvement in any conspiracy to abduct, kill or bury Mrs. McConville,” Adams said soon after his release.

He told reporters he bears no animosity toward anyone and spoke about the need to move forward.

“I’m an activist. This is my life, and I’m philosophical, and I understand that I have detractors and opponents — and I especially understand that there [are] sinister elements who are against the changes Sinn Fein and others are committed to achieving,” Adams said.

He added: “There’s only way for our society to go — and that’s forward.”

Adams had surrendered himself for questioning Wednesday evening and his detention had threatened the fragile peace in Northern Ireland, a peace Adams is in part credited with bringing about after decades of sectarian tensions.

The questioning of Adams was not unexpected. Adams said he told authorities last month that he was willing to meet with investigators.

Martin McGuinness, deputy first minister of Northern Ireland, said last week in Belfast that Adams’ arrest was unnecessary, unjustified and politically motivated.

He said that he had seen the “dark side” of Northern Ireland policing “flex its muscles in the course of the past couple of days” and that the arrest was a “‘deliberate attempt to influence the elections that are due to take place in three weeks’ time.”

A number of other people have been arrested and questioned in the investigation into McConville’s abduction and killing.

One man has been charged with aiding and abetting the crime. He denies wrongdoing.

The IRA admitted in 1999 to killing a number of people who have become known as “The Disappeared,” those who vanished during the so-called Troubles, a 30-year conflict between Protestant loyalists who wanted to stay part of the United Kingdom and Catholic nationalists who wanted to see the north united with Ireland.

Among the victims was McConville, 37, whose remains were found partially buried on a beach in County Louth in 2003. She died of a single gunshot wound to the back of the head.